Method for fabricating magnetic core

ABSTRACT

A method for fabricating a magnetic core includes depositing a magnetic layer on a dielectric layer, forming a first photoresist layer on the magnetic layer and patterning the first photoresist layer, etching the magnetic layer through the patterned first photoresist layer, in which a first section of the magnetic layer exposed by the first photoresist layer remains on the dielectric layer after the magnetic layer is etched, removing the patterned first photoresist layer, forming a second photoresist layer on the magnetic layer and patterning the second photoresist layer, etching the magnetic layer through the patterned second photoresist layer, and removing the second photoresist layer.

PRIORITY CLAIM AND CROSS-REFERENCE

The present application is a divisional of U.S. application Ser. No.14/632,519, filed Feb. 26, 2015, which is herein incorporated byreference in its entirety.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experienced rapidgrowth. Technological advances in IC materials and design have producedgenerations of ICs where each generation has smaller and more complexcircuits than the previous generation. However, these advances haveincreased the complexity of processing and manufacturing ICs and, forthese advances to be realized, similar developments in IC processing andmanufacturing are needed.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a cross-sectional view of an ideal embodiment of an inductor.

FIG. 2 is a cross-sectional view of a real embodiment of a conventionalinductor.

FIG. 3 is a cross-sectional view of different steps of a method forfabricating a magnetic core, in accordance with some embodiments.

FIG. 4 is a cross-sectional view of different steps of the method forfabricating the magnetic core, in accordance with some embodiments.

FIG. 5 is a cross-sectional view of different steps of the method forfabricating the magnetic core, in accordance with some embodiments.

FIG. 6 is a cross-sectional view of an inductor, in accordance with someembodiments.

FIG. 7 is a cross-sectional view of the inductor, in accordance withsome embodiments.

FIG. 8 is a cross-sectional view of the inductor, in accordance withsome embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Inductors are used in a wide array of applications such as signalprocessing, noise filtering, power generation, electrical transmissionsystems etc. In order to provide more compact and more efficientinductors, the electrically conducting winding of the inductor may bearranged around an elongated magnetically conducting core, i.e. amagnetic core. The magnetic core is made of a material presenting ahigher permeability than air wherein the magnetic core may enable aninductor of increased inductance. Magnetic cores are available in alarge variety of designs and materials, each having their specificadvantages and disadvantages. However, due to the increasing demand forinductors in different applications requiring less space there is stilla need for inductors and magnetic cores having a compact and efficientdesign and thereby being usable in a wide range of applications.

FIG. 1 is a cross-sectional view of an ideal embodiment of an inductor.The inductor 10 includes a substrate 11, a bottom conductive layer 12formed on the substrate 11, a bottom dielectric layer 13 formed on thebottom conductive layer 12, a magnetic core 14 formed on the bottomdielectric layer 13, a top dielectric layer 15 formed on the magneticcore 14, and a top conductive layer 16 formed on the top dielectriclayer 15.

In the ideal embodiment, the magnetic core 14 is in a shape ofrectangle. Namely, the volume loss when the magnetic core 14 is made canbe ignored. The bottom conductive layer 12 and the top conductive layer16 are patterned and are divided into a plurality of strips. The stripedbottom conductive layer 12 and the striped top conductive layer 16 forma spiral structure winding on the magnetic core 14.

However, the magnetic core 14 is made of magnetic materials, such ascobalt zirconium tantalum (CZT), nickel iron (NiFe), or iron nitride(FeN). The magnetic materials are difficult to be dry etched. Therefore,a wet etching process is utilized in forming the magnetic core 14.

FIG. 2 is a cross-sectional view of a real embodiment of a conventionalinductor. The difference between the real embodiment and the idealembodiment is the shape of the magnetic core 14′. As described above,the magnetic core 14′ is formed by a wet etching process, which is ananisotropic etching to the magnetic materials. Anisotropic etching meansdifferent etch rates in different directions in the material. The resultof etching the magnetic core 14′ with the anisotropic etching is apyramid shaped surface, e.g. top/bottom width of the magnetic core 14′is shortened. The pyramid shaped magnetic core 14′ occurs to volume lossand leads to worse inductor performance.

In order to prevent above situation, the present disclosure provides amethod for fabricating a magnetic core by using multiple wet etchingprocesses, such that the profile of the magnetic core can be morerectangular thereby providing better inductor performance.

FIG. 3 is a cross-sectional view of different steps of a method forfabricating a magnetic core, in accordance with some embodiments. Themethod starts at step S10. Step S10 is forming a photoresist layer 150on a magnetic layer 140. The magnetic layer 140 is formed on alamination structure 100. The lamination structure 100 includes asubstrate 110, a conductive layer 120 formed on the substrate 110, and adielectric layer 130 formed on the conductive layer 120.

The substrate 110 is made of, for example, silicon; a compoundsemiconductor, such as silicon carbide, indium arsenide, or indiumphosphide; or an alloy semiconductor, such as silicon germanium carbide,gallium arsenic phosphide, or gallium indium phosphide. The conductivelayer 120 is made of conductive material, for example, W, Co, Al, or Cu.The conductive layer 120 can be formed by a deposition process. Thedielectric layer 130 may have a dielectric constant greater than about3.5. The dielectric layer 130 is made of, for example, silicon nitride(SiN), silicon carbide (SiC), nitrogen-doped silicon carbide (SiC:N,also known as NDC), silicon oxynitride (SiON), oxygen-doped siliconcarbide (SiC:O, also known as ODC), or silicon oxide (SiO₂). Thedielectric layer 130 is formed by, for example low-pressure chemicalvapor deposition (LPCVD). The magnetic layer 140 is made of magneticmaterials, such as cobalt zirconium tantalum (CZT), nickel iron (NiFe),or iron nitride (FeN).

The photoresist layer 150 is patterned by a lithography process to forma feature on the magnetic layer 140. The pattern of the photoresistlayer 150 is formed in accordance with a predetermined size of themagnetic core. The lithography process may include photoresist coating,exposing, post-exposure baking, and developing. The lithography processused to form the photoresist pattern may include photoresist coating,exposing, post-exposure baking, and developing. The lithography processmay additionally include soft baking, mask aligning, and/or hard baking.The lithography process may utilize other exposing modes ortechnologies, such as on-axis, off-axis, quadripole, or dipole exposuretechnologies. The optical exposing process may alternatively beimplemented or replaced by other proper methods such as masklesslithography, electron-beam writing, ion-beam writing, and molecularimprint techniques.

Step S20 is etching the magnetic layer 140. The magnetic layer 140 isetched by a wet etching process. The wet etching process includesplacing the lamination structure 100, the magnetic layer 140 and thephotoresist layer 150 thereon into an acid. The acid can include organicacid, such as benzenedicarboxylic acid, naphthalenedicarboxylic acid,benzenetricarboxylic acid, naphthalenetricarboxylic acid,pyridinedicarboxylic acid, bipyridyldicarboxylic acid, formic acid,oxalic acid, malonic acid, succinic acid, glutaric acid, hexanedioicacid, heptanedioic acid and cyclohexyldicarboxylic acid, etc. The acidcan include inorganic acid, such as HF, HCl, HBr, HI, HNO₃, H₃PO₄,H₂SO₄, HClO₄, or a mixture thereof.

In this step, the magnetic layer 140 is etched partially. There is stilla magnetic layer 140 completely covering the dielectric layer 130 afterthe magnetic layer 140 is wet etched. The portion of the magnetic layer140 covered by the photoresist layer 150 has a maximum thickness t₁, theportion of the magnetic layer 140 exposed of the photoresist layer 150has a minimum thickness t₂, and the thickness of the magnetic layer 140is gradually decreased from t₁ to t₂ at the edge under the photoresistlayer 150. The etching ratio of the magnetic layer 140 is controlled bythe time being placing in the acid.

Step S30 is removing the photoresist layer 150. The photoresist layer150 is removed by a photoresist stripping process. The photoresistprocess can be performed by one or more wet stripping processes or oneor more dry stripping processes. The magnetic layer 140 includes threesections 142, 144, 146, in which the section 142 has a substantiallyuniform thickness t₁, the section 146 has a substantially uniformthickness t₂, and the section 144 bridges the section 142 and thesection 146. The thickness t₁ of the section 142 is greater than thethickness of the section 144, and the thickness of the section 144 isgreater than the thickness t₂ of the section 146.

Step S40 is forming another photoresist layer 160 on the magnetic layer140. The photoresist layer 160 is defined by the same mask of definingthe photoresist layer 150. Namely, the pattern and the position of thephotoresist layer 160 is substantially the same as that of thephotoresist layer 150. The sections 142 and 144 are once again coveredby the photoresist layer 160, and the section 146 is exposed of thephotoresist layer 160.

Step S50 is etching the magnetic layer 140. The magnetic layer 140 isetched by a wet etching process. In some embodiments, the acid utilizedin step S50 is substantially the same as the acid utilized in step S20.In some embodiments, the acid utilized in step S50 is different from theacid utilized in step S20. The section 146 of the magnetic layer 140 isremoved from the dielectric layer 130. The dielectric layer 130uncovered by the photoresist layer 160 is exposed of the magnetic layer140. The section 144 of the magnetic layer 140 is wet etched and has atleast two slopes at the edge of the section 144. The section 142 of themagnetic layer 140 is covered by the photoresist layer 160, and thesection 142 still has the uniform thickness t₁.

The time of the wet etching processes in step S20 and step S50 decidesthe shape of the magnetic layer 140. More particularly, the time of thewet etching processes in step S20 and step S50 decides the shape of thesection 144, which is located at the edge of the magnetic layer 140. Insome embodiments, the section 144 includes a bottom portion 141 and atop portion 143 disposed on and connected to the bottom portion 141. Thebottom portion 141 is mainly wet etched by step S50. The top portion 143is mainly wet etched by both step S20 and step S50. The side surface ofthe top portion 143 is steeper than that of the bottom portion 141. Thebottom portion 141 has a gradual side surface since the top portion 143has a steep side surface. In some embodiments, the bottom portion 141has an inclined side surface, and the top portion 143 has a curve sidesurface. The width w₁ of the bottom potion 141 extended from the section142 is also greater than the width w₂ of the top portion 143 extendedfrom the section 142. The bottom portion 141 has a thickness t₃, and thetop portion 143 has a thickness t₄. The sum of the thickness t₃ and thethickness t₄ is substantially equals to the thickness t₁ of the section142. The ratio of the thickness t₃ to the thickness t₄ is determined bythe time of step S20 and step S50. The ratio of the thickness t₃ to thethickness t₄ is in a range from about 2/3 to about 3/2. In someembodiments, the ratio of the thickness t₃ to the thickness t₄ is in arange from about 3/7 to about 7/3. If the ratio is higher or lower thanabove ratio, the shape of the section 144 would be in a shape oftriangle, and the section 144 would have greater width extended from thesection 142, such situation is unwanted and raises the issue of volumeloss.

Step S60 is removing the photoresist layer 160. The photoresist layer160 is removed by a photoresist stripping process. The photoresistprocess can be performed by one or more wet stripping processes or oneor more dry stripping processes. After the photoresist layer 160 isremoved, the patterned magnetic layer 140 can be utilized as themagnetic core in a semiconductor component, such as an inductor. Theshape of the patterned magnetic layer 140 is more like a rectanglerather than a triangle. Thus the inductor using the design may havelarger magnetic core, and the performance of the inductor is alsoimproved.

FIG. 4 is a cross-sectional view of different steps of the method forfabricating the magnetic core, in accordance with some embodiments. Thestep S10 to step S30 are substantially the same as the step S10 to stepS30 discussed in FIG. 3. The differences between FIG. 4 and FIG. 3starts at step S40′. Step S40′ is forming another photoresist layer 170on the magnetic layer 140. The photoresist layer 170 utilized in stepS40′ is different from the photoresist layer utilized in step S10. Thephotoresist layer 150 and the photoresist layer 170 are defined bydifferent masks.

In step S40′, the feature of the photoresist layer 170 is larger thanthe feature of the photoresist layer 150. The magnetic layer 140includes three sections 142, 144, 146, in which the section 142 has asubstantially uniform thickness t₁, the section 146 has a substantiallyuniform thickness t₂, and the section 144 bridges the section 142 andthe section 146. The thickness t₁ of the section 142 is greater than thethickness of the section 144, and the thickness of the section 144 isgreater than the thickness t₂ of the section 146. The photoresist layer170 mainly covers on the section 142 and 144, and an edge portion of thephotoresist layer 170 covers on the section 146. The width w₃ of thephotoresist layer 170 covering on the section 146 is in a range fromabout 1 μm to about 5 μm.

Step S50′ is etching the magnetic layer 140. The magnetic layer 140 isetched by a wet etching process. In some embodiments, the acid utilizedin step S50′ is substantially the same as the acid utilized in step S20.In some embodiments, the acid utilized in step S50′ is different fromthe acid utilized in step S20. The section 146 of the magnetic layer 140is removed from the dielectric layer 130. The dielectric layer 130uncovered by the photoresist layer 170 is exposed of the magnetic layer140. The section 144 of the magnetic layer 140 is wet etched and has atleast two slopes at the edge of the section 144. The section 142 of themagnetic layer 140 is covered by the photoresist layer 170, and thesection 142 still has the uniform thickness t₁.

The time of the wet etching processes in step S20 and step S50′ decidesthe shape of the magnetic layer 140. More particularly, the time of thewet etching processes in step S20 and step S50′ decides the shape of thesection 144, which is located at the edge of the magnetic layer 140. Insome embodiments, the section 144 includes a bottom portion 141 and atop portion 143 disposed on and connected to the bottom portion 141. Thebottom portion 141 is mainly wet etched by step S50′. The top portion143 is mainly wet etched by both step S20 and step S50′. The slope ofthe bottom portion 141 is smaller than the slope of the top portion 143.The bottom portion 141 has a gradual side surface since the top surface143 has a steep side surface. In some embodiments, the bottom portion141 has an inclined side surface, and the top portion 143 has a curveside surface.

The width w₁ of the bottom potion 141 extended from the section 142 isalso greater than the width w₂ of the top portion 143 extended from thesection 142. The width w₂ is greater than that in FIG. 3. The volume ofthe section 144 is also greater than that in FIG. 3. The profile of thepatterned magnetic layer 140 is similar to a rectangle.

The bottom portion 141 has a thickness t₃, and the top portion 143 has athickness t₄. The sum of the thickness t₃ and the thickness t₄ issubstantially equals to the thickness t₁ of the section 142. The ratioof the thickness t₃ to the thickness t₄ is determined by the time ofstep S20 and step S50′. The ratio of the thickness t₃ to the thicknesst₄ is in a range from about 2/3 to about 3/2. In some embodiments, theratio of the thickness t₃ to the thickness t₄ is in a range from about3/7 to about 7/3. If the ratio is higher or lower than above ratio, theshape of the section 144 would be in a shape of triangle, and thesection 144 would have greater width extended from the section 142, suchsituation is unwanted and raises the issue of volume loss.

Step S60′ is removing the photoresist layer 170. The photoresist layer170 is removed by a photoresist stripping process. The photoresistprocess can be performed by one or more wet stripping processes or oneor more dry stripping processes. After the photoresist layer 170 isremoved, the patterned magnetic layer 140 can be utilized as themagnetic core in a semiconductor component, such as an inductor. Theshape of the patterned magnetic layer 140 is more like a rectangle thanthat in FIG. 3. The inductor using the design may have larger magneticcore, and the performance of the inductor is also improved.

FIG. 5 is a cross-sectional view of different steps of the method forfabricating the magnetic core, in accordance with some embodiments. Themethod may optionally include step S70 to step S90, which follow afterthe step S10 to step S40 discussed in FIG. 3 (or step S10 to step S40′discussed in FIG. 4).

Step S70 is etching the magnetic layer 140. The magnetic layer 140 isetched by a wet etching process. In some embodiments, the acid utilizedin step S70 is substantially the same as the acid utilized in step S20.In some embodiments, the acid utilized in step S70 is different from theacid utilized in step S20. The magnetic layer 140 is covered by thephotoresist layer 160, which is substantially the same as thephotoresist layer 140 (or the photoresist layer 170, which has largerfeature than that of the photoresist layer 140) on the magnetic layer140. More particularly, the sections 142 and 144 are covered by thephotoresist layer 160, and the section 146 is exposed of the photoresistlayer 160. The sections 144 and 146 are wet etched. The section 146becomes thinner and has a minimum thickness t₅, the section 142 coveredby the photoresist layer 160 has a maximum thickness t₁, and the section144 bridges the sections 142 and 146. The section 144 under the edge ofthe photoresist layer 160 includes a bottom portion 141 and the topportion 143, in which the bottom portion 141 connects the section 146 tothe top portion 143. The width w₁ of the bottom portion 141 extendedfrom the section 142 is greater than the width w₂ of the top portionextended from the section 142.

Step S80 is removing the photoresist layer 160. The photoresist layer160 is removed by a photoresist stripping process. The photoresistprocess can be performed by one or more wet stripping processes or oneor more dry stripping processes. The magnetic layer 140 includes thesection 142 with the uniform thickness t₁, the section 146 with theuniform thickness t₅, and the section 144 bridges the sections 142 and146. The section 144 includes the bottom portion 141 and the top portion143. The bottom portion 141 has a gradual side surface since the topportion 143 has a steep side surface. In some embodiments, the bottomportion 141 has an inclined side surface, and the top portion 143 has acurve side surface. Step S90 is forming yet another photoresist layer180 on the magnetic layer 140. The magnetic layer 140 includes thesection 142, the section 144, and the section 146. The photoresist layer180 covers the sections 142 and 144. The section 146 is exposed of thephotoresist layer 180. The feature of the photoresist layer 180 can bethe same as or larger than that of photoresist layer 160.

Step S100 is etching the magnetic layer 140. The magnetic layer 140 isetched by a wet etching process. In some embodiments, the acid utilizedin step S100 is substantially the same as the acid utilized in step S20and step S50 (step S50′). In some embodiments, the acid utilized in stepS100 is different from that in step S20 and step S50 (step S50′). Thesection 146 exposed of the photoresist layer 180 is removed, and thedielectric layer 130 uncovered by the photoresist layer 180 is exposed.Meanwhile, the edge of the section 144 under the edge of the photoresistlayer 180 is removed.

The section 144 now includes three portions 145, 147, 149, in which theportion 145 is disposed on the dielectric layer 130, the portion 147 isdisposed on the portion 145, and the portion 149 is disposed on theportion 147. Namely, the portion 145 can be regarded as a bottomportion, the portion 147 can be regarded as a middle portion, and theportion 149 can be regarded as a top portion. The top portion 149 ismainly wet etched by the step S20, the step S50 (S50′), and the stepS100, and the top potion 149 has a curve side surface. The middleportion 147 is mainly wet etched by the step S50 (S50′) and the stepS100, and the middle portion 147 has a curve side surface. The bottomportion 145 is mainly wet etched by the step S100, and the bottomportion 145 has an inclined side surface. The width of the bottomportion extended from the section 142 is shortened. The thickness of thebottom portion 145, the middle portion 147, and the top portion 149 canbe control by the time of wet etching the magnetic layer 140 in stepS20, step S50 (S50′), and step S100.

Step S110 is removing the photoresist layer 180. The photoresist layer180 is removed by a photoresist stripping process. The photoresistprocess can be performed by one or more wet stripping processes or oneor more dry stripping processes. After the photoresist layer 180 isremoved, the patterned magnetic layer 140 can be utilized as themagnetic core in a semiconductor component, such as an inductor. Thepatterned magnetic layer 140 includes the section 142 with the uniformthickness and the section 144 connected to the section 142. The section142 is surrounded by the section 144. The section 144 has more thanthree different slopes. The shape of the patterned magnetic layer 140provided by step S110 is more like a rectangle since the width of thebottom portion 145 and the middle portion 147 are shortened by multiplewet etching processes. The volume of the magnetic core (the patternedmagnetic layer 140) is enhanced. The performance of the inductor usingthe magnetic core is also improved.

FIG. 6 is a cross-sectional view of an inductor, in accordance with someembodiments. The inductor 200 includes a substrate 210, a bottomconductive layer 220 formed on the substrate 210, a bottom dielectriclayer 230 formed on the bottom conductive layer 220, a top dielectriclayer 250 formed on the magnetic core 240, and a top conductive layer260 formed on the top dielectric layer 250.

The substrate 210 is made of, for example, silicon; a compoundsemiconductor, such as silicon carbide, indium arsenide, or indiumphosphide; or an alloy semiconductor, such as silicon germanium carbide,gallium arsenic phosphide, or gallium indium phosphide. The bottomconductive layer 220 and the top conductive layer 260 are made ofconductive material, for example, W, Co, Al, or Cu. The bottomdielectric layer 230 and the top dielectric layer 250 may have adielectric constant greater than about 3.5. The bottom dielectric layer230 and the top dielectric layer 250 are made of, for example, siliconnitride (SiN), silicon carbide (SiC), nitrogen-doped silicon carbide(SiC:N, also known as NDC), silicon oxynitride (SiON), oxygen-dopedsilicon carbide (SiC:O, also known as ODC), or silicon oxide (SiO₂). Themagnetic core 240 is made of magnetic materials, such as cobaltzirconium tantalum (CZT), nickel iron (NiFe), or iron nitride (FeN). Thebottom conductive layer 220 and the top conductive layer 260 form awinding wire wound on the magnetic core 240.

The magnetic core 240 is fabricated by the method disclosed in FIG. 3.The magnetic core 240 includes a center section 242 and an edge section244 connected to the center section 242. The center section 242 issurrounded by the edge section 244. The edge section 244 includes atleast two different slopes. The edge section 244 includes a bottomportion 241 and a top portion 243 disposed on and connected to thebottom portion 241. The center section 242 has a substantially uniformthickness. The width of the bottom portion 241 extended from the centersection 242 is greater than the width of the top portion 243 extendedfrom the center section 242. The bottom portion 241 has a gradual sidesurface since the top portion 243 has a steep side surface. In someembodiments, the bottom portion 241 has an inclined side surface, andthe top portion 143 has a curve side surface. The ratio of the thicknessof the bottom portion to the thickness of the top portion is in a rangefrom about 2/3 to about 3/2. In some embodiments, the ratio is in arange from about 3/7 to about 7/3. If the ratio is higher or lower thanabove ratio, the shape of the edge section 244 would be in a shape oftriangle, and the edge section 244 would have greater width extendedfrom the center section 242, such situation is unwanted and raises theissue of volume loss. The existence of the top portion 243 enlarges thevolume of the magnetic core 240 (comparing with the transitionalmagnetic core 14′ disclosed in FIG. 2). Thus the performance of theinductor 200 is improved.

FIG. 7 is a cross-sectional view of the inductor, in accordance withsome embodiments. The difference between the FIG. 7 and FIG. 6 is thatthe magnetic core 240 of FIG. 7 is fabricated by the method disclosed inFIG. 4. The magnetic core 240 includes a center section 242 and an edgesection 244 connected to the center section 242. The center section 242is surrounded by the edge section 244. The edge section 244 includes atleast two different slopes. The edge section 244 includes a bottomportion 241 and a top portion 243 disposed on and connected to thebottom portion 241. The center section 242 has a substantially uniformthickness. The width of the bottom portion 241 extended from the centersection 242 is shorter than that disclosed in FIG. 6, but still greaterthan the width of the top portion 243 extended from the center section242. The bottom portion 241 has a gradual side surface since the topportion 243 has a steep side surface. In some embodiments, the bottomportion 241 has an inclined side surface since the top portion 243 has acurve side surface. The ratio of the thickness of the bottom portion tothe thickness of the top portion is in a range from about 2/3 to about3/2. In some embodiments, the ratio is in a range from about 3/7 toabout 7/3. If the ratio is higher or lower than above ratio, the shapeof the edge section 244 would be in a shape of triangle, and the edgesection 244 would have greater width extended from the center section242, such situation is unwanted and raises the issue of volume loss. Theshape of the magnetic core 240 is more like a rectangle, such that themagnetic core 240 has less volume loss comparing with the transitionalmagnetic core 14′ disclosed in FIG. 2. Thus the performance of theinductor 200 is improved.

FIG. 8 is a cross-sectional view of the inductor, in accordance withsome embodiments. The difference between the FIG. 8 and FIG. 6 is thatthe magnetic core 240 of FIG. 8 is fabricated by the method disclosed inFIG. 5. The magnetic core 240 includes the center section 242 and theedge section 244 connected to the center section 242. The edge section244 includes at least three different slopes. The edge section 244includes a bottom portion 245, a middle portion 247, and a top portion249. The bottom portion 245 is disposed on the bottom dielectric layer230, the middle portion 247 is disposed on the bottom portion, and thetop portion 249 is disposed on the middle portion 247. The width of thebottom portion 245 extended from the center section 242 is greater thanthe width of the middle portion 247 extended from the center section242. The width of the middle portion 247 extended from the centerportion 242 is greater than the width of the top portion 249 extendedfrom the center portion 242. The bottom portion 245 has an inclined sidesurface. The middle portion 247 has a curve surface. The top portion hasa curve surface. The shape of the magnetic core 240 is similar to arectangle. The volume loss of the magnetic core 240 is very small, thusthe inductor 200 using the magnetic core 240 has good performance.

The method for fabricating a magnetic core includes using multiple wetetching processes, such that the profile of the magnetic core can bemore rectangular thereby providing better inductor performance.

An aspect of the disclosure provides a method for fabricating a magneticcore. The method includes depositing a magnetic layer on a dielectriclayer, forming a first photoresist layer on the magnetic layer andpatterning the first photoresist layer, etching the magnetic layerthrough the patterned first photoresist layer, in which a first sectionof the magnetic layer exposed by the first photoresist layer remains onthe dielectric layer after the magnetic layer is etched, removing thepatterned first photoresist layer, forming a second photoresist layer onthe magnetic layer and patterning the second photoresist layer, etchingthe magnetic layer through the patterned second photoresist layer, andremoving the second photoresist layer.

According to some embodiments, the first photoresist layer and thesecond photoresist layer are patterned using the same mask.

According to some embodiments, a portion of the patterned secondphotoresist layer covering a second section of the magnetic layer islarger than a portion of the patterned first photoresist layer coveringthe second section of the magnetic layer.

According to some embodiments, the first section of the magnetic layerexposed by the patterned second photoresist layer is removed from thedielectric layer after etching the magnetic layer through the patternedsecond photoresist layer.

According to some embodiments, the first section of the magnetic layerexposed by the patterned second photoresist layer remains on thedielectric layer after etching the magnetic layer through the patternedsecond photoresist layer.

According to some embodiments, the method includes forming a thirdphotoresist layer on the magnetic layer and patterning the thirdphotoresist layer, etching the magnetic layer through the patternedthird photoresist layer, in which the first section of the magneticlayer exposed by the patterned third photoresist layer is removed fromthe dielectric layer after etching the magnetic layer through thepatterned third photoresist layer, and removing the patterned thirdphotoresist layer.

According to some embodiments, the first photoresist layer, the secondphotoresist layer, and the third photoresist layer are patterned usingthe same mask.

According to some embodiments, etching the magnetic layer through thepatterned first photoresist layer is performed using a wet etchingprocess.

Another aspect of the disclosure provides a method for fabricating amagnetic core. The method includes depositing a magnetic layer over adielectric layer, etching the magnetic layer through a first patternedphotoresist layer, in which a first section of the magnetic layer isexposed by the first patterned photoresist layer, and a second sectionof the magnetic layer is covered by the first patterned photoresistlayer, and etching the first section of the magnetic layer through asecond patterned photoresist layer, wherein the second section of themagnetic layer is covered by the second patterned photoresist layer.

According to some embodiments, the method includes removing the firstpatterned photoresist layer prior to etching the first section of themagnetic layer through the second patterned photoresist layer.

According to some embodiments, the first section of the magnetic layeris removed from the dielectric layer after etching the first section ofthe magnetic layer through the second patterned photoresist layer.

According to some embodiments, the first section of the magnetic layerremains on the dielectric layer after etching the first section of themagnetic layer through the second patterned photoresist layer.

According to some embodiments, etching the magnetic layer through thefirst patterned photoresist layer is performed using a wet etchingprocess.

According to some embodiments, etching the first section of the magneticlayer through the second patterned photoresist layer is performed usinga wet etching process.

According to some embodiments, the first patterned photoresist layer andthe second patterned photoresist layer are patterned using the samemask.

According to some embodiments, a portion of the second patternedphotoresist layer covering the second section of the magnetic layer islarger than a portion of the first patterned photoresist layer coveringthe second section of the magnetic layer.

Another aspect of the disclosure provides a method for fabricating amagnetic core. The method includes depositing a magnetic layer over adielectric layer, etching the magnetic layer, such that the magneticlayer having a first section and a second section, and the secondsection is thicker than the first section, forming a first patternedphotoresist layer over the second section, wherein the first section isexposed by the first patterned photoresist layer, etching the firstsection through the first patterned photoresist layer, and removing thefirst patterned photoresist layer.

According to some embodiments, the first section is removed from thedielectric layer after etching the first section through the firstpatterned photoresist layer.

According to some embodiments, the first section remains on thedielectric layer after etching the first section through the firstpatterned photoresist layer.

According to some embodiments, the method includes forming a secondpatterned photoresist layer over the second section, in which the firstsection is exposed by the second patterned photoresist layer, andetching the first section through the second patterned photoresistlayer.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method for fabricating a magnetic core,comprising: depositing a magnetic layer on a dielectric layer; forming afirst photoresist layer on the magnetic layer and patterning the firstphotoresist layer; etching the magnetic layer through the patternedfirst photoresist layer, wherein a first section of the magnetic layerexposed by the patterned first photoresist layer remains on thedielectric layer after etching the magnetic layer; removing thepatterned first photoresist layer; forming a second photoresist layer onthe magnetic layer and patterning the second photoresist layer such thatthe patterned second photoresist layer has a curve portion; etching themagnetic layer through the patterned second photoresist layer such thatthe curve portion of the patterned second photoresist layer suspendswithout support above the magnetic layer; and removing the patternedsecond photoresist layer.
 2. The method of claim 1, wherein the firstphotoresist layer and the second photoresist layer are patterned usingthe same mask.
 3. The method of claim 1, wherein a portion of thepatterned second photoresist layer covering a second section of themagnetic layer is larger than a portion of the patterned firstphotoresist layer covering the second section of the magnetic layer. 4.The method of claim 1, wherein the first section of the magnetic layerexposed by the patterned second photoresist layer is removed from thedielectric layer after etching the magnetic layer through the patternedsecond photoresist layer.
 5. The method of claim 1, wherein the firstsection of the magnetic layer exposed by the patterned secondphotoresist layer remains on the dielectric layer after etching themagnetic layer through the patterned second photoresist layer.
 6. Themethod of claim 5, further comprising: forming a third photoresist layeron the magnetic layer and patterning the third photoresist layer;etching the magnetic layer through the patterned third photoresistlayer, wherein the first section of the magnetic layer exposed by thepatterned third photoresist layer is removed from the dielectric layerafter etching the magnetic layer through the patterned third photoresistlayer; and removing the patterned third photoresist layer.
 7. The methodof claim 6, wherein the first photoresist layer, the second photoresistlayer, and the third photoresist layer are patterned using the samemask.
 8. The method of claim 1, wherein etching the magnetic layerthrough the patterned first photoresist layer is performed using a wetetching process.
 9. A method for fabricating a magnetic core,comprising: depositing a magnetic layer over a dielectric layer; forminga first patterned photoresist layer over the magnetic layer, wherein afirst section of the magnetic layer is exposed by the first patternedphotoresist layer, and a second section of the magnetic layer is coveredby the first patterned photoresist layer; etching the first section ofthe magnetic layer through the first patterned photoresist layer;forming a second patterned photoresist layer over the magnetic layer,wherein the first section of the magnetic layer is exposed by the secondpatterned photoresist layer, and the second section of the magneticlayer is covered by the second patterned photoresist layer; and etchingagain the first section of the magnetic layer through the secondpatterned photoresist layer.
 10. The method of claim 9, furthercomprising removing the first patterned photoresist layer prior toetching the first section of the magnetic layer through the secondpatterned photoresist layer.
 11. The method of claim 9, wherein thefirst section of the magnetic layer is removed from the dielectric layerafter etching the first section of the magnetic layer through the secondpatterned photoresist layer.
 12. The method of claim 9, wherein thefirst section of the magnetic layer remains on the dielectric layerafter etching the first section of the magnetic layer through the secondpatterned photoresist layer.
 13. The method of claim 9, wherein etchingthe magnetic layer through the first patterned photoresist layer isperformed using a wet etching process.
 14. The method of claim 9,wherein etching the first section of the magnetic layer through thesecond patterned photoresist layer is performed using a wet etchingprocess.
 15. The method of claim 9, wherein the first patternedphotoresist layer and the second patterned photoresist layer arepatterned using the same mask.
 16. The method of claim 9, wherein aportion of the second patterned photoresist layer covering the secondsection of the magnetic layer is larger than a portion of the firstpatterned photoresist layer covering the second section of the magneticlayer.
 17. A method for fabricating a magnetic core, comprising:depositing a magnetic layer over a dielectric layer; etching themagnetic layer, such that the magnetic layer having a pair of firstsections and a second section between the first sections, and the secondsection is thicker than the first sections; forming a first patternedphotoresist layer over the second section, wherein the first sectionsare exposed by the first patterned photoresist layer; etching the firstsections through the first patterned photoresist layer such that atleast one of the first sections has a convex sidewall; and removing thefirst patterned photoresist layer.
 18. The method of claim 17, whereinthe first sections are removed from the dielectric layer after etchingthe first sections through the first patterned photoresist layer. 19.The method of claim 17, wherein the first sections remain on thedielectric layer after etching the first sections through the firstpatterned photoresist layer.
 20. The method of claim 19, furthercomprising: forming a second patterned photoresist layer over the secondsection, wherein the first sections are exposed by the second patternedphotoresist layer; and etching the first sections through the secondpatterned photoresist layer.